This invention relates to metal working operations and more particularly to lubricants for use during such operations. In its broadest sense, it comprises compositions and methods for lubricating metal during working thereof and metal workpieces having on the surface thereof a film of a lubricant composition.
Particularly in the case of galvanized steel which is being widely used for metal forming of automotive body component, conventional overbased sulfonates can provide a high degree of lubricity for drawing and forming operations. Many automotive plants are moving towards the use of pre-lubrication of sheet metal which requires that both the anti-stain and anti-corrosion components as well as the lubricity additives be combined and applied at the steel mill. Pre lubricants are required to provide high levels of corrosion protection and lubrication in a low viscosity easily cleaned oil base.
The current practices using galvanized steel for automotive applications include the use of both mill oils to prevent corrosion and staining, and drawing compounds to improve drawability. The prelube concept is to provide corrosion protection and the required lubricity for the metal forming operations. Thus, substituting a lubricant for both mill oil and drawing compound would be useful and efficient.
It is of critical importance that stain and corrosion protection be provided for the galvanized surface, because even the slightest corrosion of the zinc will cause cosmetic defects which become evident after final paint application. Once the paint has been applied and cured on a defect-free galvanized surface, the zinc provides the necessary rust protection for the steel substrate.
This increasing attention to the corrosion resistance of vehicles has led to extensive use of two sided electrogalvanized steel. However, only limited work on drawing lubricants for electrogalvanized steel has been done. In recent work, electrogalvanized steel sheet was drawn into a cylindrical cup using various lubricants. Among extreme-pressure agents, the effectiveness of chlorinated paraffin was prominent as well as calcium overbased sulfonate. Chlorinated paraffin has been widely used for drawing sheet steel but increasing government regulations may restrict its use in the future.
Up to now it has not been possible to combine overbased calcium sulfonates with oxidate anti-corrosion additives due to reactions which deactivate the sulfonate and which gel or destabilize the mixture.